1. Field of the Invention
The present invention relates to a connection between a mobile node and a correspondent node in mobile communications networks, and more particularly, to a system and a method for deleting tunnelling when a correspondent node is connected to a mobile node that has moved to a different network (or foreign network).
2. Description of the Related Art
A mobile node (also called an MN) is a host or router that can change its network connection location. A correspondent node (also called a CN) is a host or router that communicates with the mobile node.
When the mobile node moves to a different network, it automatically creates a new address. The created address is referred to as a care of address (hereinafter, referred to as a COA). When an address of the mobile node in a home network is referred to as a home address. Both the COA and the home address are Internet protocol (hereinafter, referred to as IP) addresses of the mobile node, but they have different network prefix information.
When the mobile node creates the COA, a home agent (hereinafter, referred to as an HA) of the home network of the mobile node binds the COA with the home address of the mobile node, thereby managing an address of the mobile node. At this time, an IP address of the mobile node, which is registered in a domain name service (hereinafter, referred to as a DNS) server, is the home address.
Hence, when a new correspondent node attempts to connect to the mobile node that has moved to the different network, the correspondent node obtains the home address of the mobile node from the DNS server. As a result, a packet destined to the mobile node by the correspondent node is intercepted by the home agent and is then tunneled to a current location of the mobile node.
FIG. 1 illustrates a network environment for explaining a conventional method for connecting between a mobile node and a correspondent node when a new correspondent node attempts to connect to a mobile node that has moved to a different network.
A subnet 1 of FIG. 1 is a home network of a mobile node MN. The home network can communicate with a correspondent node using a home address of the mobile node MN. A subnet 2 is any one of a plurality of different networks.
When the mobile node MN moves from the home network, i.e., the subnet 1, to the different network, i.e., the subnet 2, it creates a new COA having a network prefix of the subnet 2. The mobile node MN notifies a home agent HA of the subnet 1 of the created COA. The home agent HA of the subnet 1 binds the created COA of the subnet 2 with the home address of the mobile node MN of the subnet 1, thereby managing an address of the mobile node MN.
While the home agent HA of the subnet 1 manages the address of the mobile node MN, if a new correspondent node CN transmits a DNS query message including a domain name of the mobile node MN to a DNS server 100 so as to connect to the mobile node MN, the DNS server 100 transmits a DNS reply message including an IP address corresponding to the domain name to the new correspondent node CN.
Thus, the new correspondent node CN obtains the IP address of the mobile node MN. However, as pointed out above, the obtained IP address of the mobile node MN is the home address of the mobile node MN. Thus, if the new correspondent node CN transmits a packet using the obtained IP address, the home agent HA of the subnet 1 intercepts the packet and transmits the packet to the mobile node MN connected to the subnet 2 by means of tunneling.
After receiving the tunneled packet, the mobile node MN determines that the new correspondent node CN has no binding information, then transmits a binding update message to the new correspondent node CN, and performs a route optimization process which notifies the new correspondent node CN of the COA of the mobile node MN. After completion of the route optimization process, the mobile node MN and the new correspondent node CN can directly transmit and receive the packet without involving the home agent HA of the subnet 1.
As such, according to prior art, when the new correspondent node CN attempts to connect to the mobile node MN that has moved to the different network, the home agent HA intercepts a packet and transmits the packet to the location of the mobile node MN by means of tunnelling. Such packet transmission is inefficient in terms of use of a packet transmission path. This inefficiency becomes serious when a plurality of correspondent nodes CN attempts to connect to the mobile node MN. This is because the home agent HA intercepts all packets delivered by the plurality of correspondent nodes CN and tunnels the packets to the mobile node MN.
Also, if the mobile node MN receives the tunneled packets, route optimization between the correspondent node CN and the mobile node MN must be carried out, so that the packets can be transmitted and received directly between the correspondent node CN and the mobile node MN. According to prior art, a plurality of packets must be transmitted so as to provide a network environment where packet transmission is performed directly between the correspondent node CN and the mobile node MN that has moved to the different network.